Certain types of conventional stormwater drain inserts include a layer of water permeable fabric that captures sediment and other contaminants, but allows water to pass through the fabric. In some designs, a central sediment bag extends downwardly from a flat layer of the water permeable fabric. The stormwater drain inserts may be held in place within a storm chamber by the weight of a storm drain grate that presses around the periphery of the fabric layer. Braces may optionally be inserted through loops at edges of the fabric for additional stability. Slits or openings are provided at the outer edges or corners of the filter fabric to accommodate such braces. However, such slits and openings can allow untreated stormwater runoff to pass through.
In round stormwater drains, a circular metal rod may be located at a circular top edge of a sediment bag for added stability. Such rods define a specific chamber opening diameter and cannot be adjusted for different size chambers.